A programmable thermostat supports at least one attribute where each different attribute values may support different sets of thermostatic settings. The programmable thermostat may be programmed based on the different attribute values rather than on temperature set points that are traditionally mapped to programmed times. Each set may include settings for a plurality of controlled equipment including a heating/cooling system, fan, ventilator, humidifier, and/or de-humidifier. Each embodiment may support attribute values associated with an occupancy attribute (which is indicative whether or not people are occupying an environmental entity) and/or a scenario attribute (which flexibly maps different thermostatic settings to different scenario attribute values). Stored configuration data about the thermostatic settings may be organized as a tree structure, where the leaves correspond to the thermostatic settings. A programmable thermostat/ventilator controller may also instruct a ventilator system to run during an adjustable pre-occupancy purge time duration before an environmental entity is occupied.